In a semiconductor manufacturing process, since resist patterns easily collapse with miniaturization of circuit patterns, various measures have been considered. As one of the measures, a technique has been conducted, in which a resist pattern is transferred to an underlayer film formed on a semiconductor wafer (hereinafter, referred to as a “wafer”), and the pattern of the underlayer film is used as an etching mask to perform an etching of the wafer. For the underlayer film, high plasma resistance and high etching resistance are required. For example, a spin-on-carbon (SOC) film, which is formed by spin coating, has been used as the underlayer film.
The wafer coated with the SOC film is heated after a coating processing, so that a solvent remaining in the coating film is dried or a crosslinking reaction by a crosslinking agent is facilitated. At this time, a sublimate is generated from the coating film. As a heat treatment apparatus for performing such a heat treatment, for example, Japanese Patent Laid-Open Publication No. 2000-124206 discloses an apparatus in which a periphery of a hot plate that heats a substrate is blocked by a ring shutter, an inert gas is introduced into a processing space from a periphery of the ring shutter, and an heat treatment is performed while exhausting the inert gas from an upper side of a central portion of the wafer.
Recently, it has been requested that the carbon content in the SOC film be increased in order to enhance the plasma resistance of the SOC film. As a measure for increasing the carbon content, heating is performed at a temperature (350° C. to 400° C.) higher than the conventional heating temperature (300° C.). However, in a case where the heating temperature is increased, since a low molecular weight polymer is also scattered in addition to the sublimate that sublimates from the crosslinking agent contained in the SOC film, the amount of the sublimate increases. Thus, it is necessary to increase an exhaust amount in order to suppress the sublimate from leaking out from the processing container to the outside. In that case, however, an air flow reaching the central portion on the wafer surface may be increased, and the coating film may be swollen. Therefore, an in-plane uniformity of the film thickness may be deteriorated.